In the past 5 years, our Program Project team has used a systems approach to overcome the vascular and interstitial barriers impeding the delivery and efficacy of molecular medicine. We have provided novel insights into the active role of stromal cells in host-tumor interactions (PNAS, 2001;Nature, 2002), the mosaic" nature of the tumor vessel wall (PNAS, 2000), and the critical role of collagen in interstitial transport (Nature Medicine, 2003, 2004a);and we have translated these insights into a clinical trial (Nature Medicine, 2004b). Our most exciting and clinically relevant finding is that when the balance of pro- and antiangiogenic molecules is partially restored in tumors by VEGF blockade, the aberrant structure and function of the vasculature and interstitial matrix transiently become closer to that of normal tissue (Cancer Research, 2004;Cancer Cell, 2004). This "vascular normalization" concept offers an explanation for the enhanced efficacy achieved clinically when VEGF blockade is combined with chemotherapy (Nature Medicine, 2001;Science, 2005). In our proposed Program Project, we aim to address critical issues in the clinical translation of tumor anti-angiogenic therapy. The overall theme is to characterize tumor response to five antiangiogenic agents-currently in clinical testing- that differentially target the VEGF and PDGF signaling pathways. Project 1 and 2 will determine the potential of these antiangiogenic agents to induce a vascular normalization window for optimal combination with cytotoxic agents. We will attempt to improve these treatments by manipulating perivascular cell recruitment (Project 1). We will establish a "normalization index" for each antiangiogenic agent, determine chemotherapeutic agent delivery and tumor response and evaluate surrogate markers of vascular normalization (Project 2). Finally, we will elucidate the role of cytokines and proteases in the permeabilization of the collagen matrix in tumors, and aim to use relaxin or halofuginone to improve delivery of large molecular weight theraputics (Project 3). A major strength of this renewal Program is the high level of scientific interaction between the three Projects - as documented in joint publications by Project leaders over the past five years. Each Project relies upon unique in vitro and in vivo models (Nature, 2000, 2004b);powerful intravital techniques (Nature Reviews Cancer, 2002);innovative imaging technologies (Nature Medicine 2001, 2003, 2004a, 2005), mathematical modeling (Blood, 2003), and statistical support (Core A);cutting-edge molecular, cellular, and histological expertise (Core B);superb surgical and animal support (Core C);and administrative support (Core D). With this infrastructure, and the help of our clinical collaborators, we intend to develop optimal strategies for cancer therapy and to translate our scientific discoveries into clinical trials.